~ Musings on weather and science

Cooler Temperatures Coming…And Radiational Heat Loss Mysteries (Pt 3)

We are in a fairly stable weather pattern sandwiched between a low pressure center off the Pacific Northwest and a high pressure center near the Four-Corners region. That will allow some amount of cloudiness to drift up from the south, but will deny them the dynamics needed to get any precipitation from them. High temperatures will hover in the low 90s before a cold front Friday night comes through kicking up some Saturday winds and dropping our temperatures into the lower 80s which will last through Sunday.

Yesterday I said the ground can lose heat by conducting heat directly into the air. But the ground can also transfer energy (heat) directly into space by radiation. The energy bypasses the atmosphere; therefore the ground will get colder than the surrounding air. It can make for a dramatic difference.

Because of this energy transfer, the morning, ground temperature can be more than 10 degrees colder than the air temperature.

Road Weather Information System

For several years, I worked with the Nevada Department of Transportation on their Road Weather Information System (RWIS). These consisted of weather stations coupled with road sensors, which allowed road crews to remotely see when and if the roads surfaces reached the freezing point. On some nights when the air temperatures were relatively mild, ice still formed on the roads thanks to this radiational cooling effect. Many a tomato plant has been killed by frost during nights where the temperature never dropped below the 40s. And your humble meteorologist always hears about it afterward. How do clouds affect this? The answer tomorrow.